Electric furnace.



W. N. CRAFTS.

ELECTRIC FURNACE.

APPLICATION FILED OUT. 28, 1911.

Patented Aug. 12, 1913.

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ELECTRIC FURNACE,

APPLIOATION IILEDOOT. 2a, 1911.

1,069,923, Patented Aug. 12, 1913.

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of the bath of the material to be reduced,

WALTER N. CRAFTS,

OF OBERLIN, OHIO.

ELECTRIC FURNACE.

Application filed October 28, 1911.

To all whom, it may concern Be it known that I, WALTER N. CRAFTS, a citizen of the United States, residing at Oberlin, in the county of Lorain and State of Ohio, have invented a certain new and useful Improvement in Electric Furnaces, of which the following is a full, clear, and exact description, reference being had to the accompanying drawings.

This invention relates to electric furnaces of the induction type. In such furnaces it has been customary to provide an induction coil, the primary of which carries alternating current, and the secondary of which consists of an annular horizontal bath of the material to be fused, the core being vertical and surrounded by such bath.

In my invention I locate the primary coil out of the furnace basin and I arrange the secondary in an annular course, one portion of which includes fusible material in the bottom of such basin. In accomplishing this, I place the core and primary winding horizontally below the basin, so that the secondary, which surrounds the primary, lies in a vertical plane with the upper portion of its course made by a bottom portion melted or refined. The remainder of the annular secondary circuit consists of a conductor which may either fuse or remain solid. In the former case the conductor may be a portion of the material from the bath, and in such case I cause a continuous circulation of the material constituting the secondary, by reason of difference in specific gravity, owing to difference in temperature in the different legs of the secondary circuit. t will accordingly be seen that by my im' provement, not only is the bath kept unobstructed for convenient working, but it is heated from the bottom upwardly, which is a decided advantage, in circulating the metal in the bath, and, where the secondary consists of fusible material similar to that in the bath, the circulation of the secondary itself is an additional advantage in obtaining even heating. The largest part of the heat is located above the magnet and primary winding so that they do not suffer from heat. Numerous other advantages re- Specification of Letters Patent.

Patented Aug. 12,1913.

Serial No. 657,270.

sult from my improvement, several of which will be referred to hereinafter.

My invention is adapted to various types D The invention is herein illustrated in connection with a furnace of the open hearth type, which is to be taken as illustrative of any furnace.

The construction and operation are here inafter more fully explained and the essential characteristics of the invention are set.

out in the claims.

In the drawings, Figure 1 is a side elevat-ion of an open hearth furnace embodying my invention; Fig. 2 is a vertical central section through such furnace in a plane parallel with Fig. 1; Figs. 3 and 4 are horizontal sections looking downward, on correspondingly numbered lines of Fig. 2; Fig. 5 is a vertical transverse section through one of the primary windings, as indicated by the line 55 of Fig. 2.

In the particular furnace shown in the drawings, 10 represents the furnace body, which is of suitable refractory material sur rounded by a metal shell 11. In its upper portion this body is formed into a continuous, unobstructed basin or hearth 12 carrying the bath. In this basin the refining is accomplished by bringing the metal into contact with the under surface of the surmounting slag. Above the basin is an arched roof 13 and, at the side and end of the inclosed chamber and above the line of the bath, are filling openings 1% closed by suitable doors 15. Through these openings the slag forming materials for refining are added and alloy additions are made. Accordingly, the basin, in the present apparatus, is similar in use and operation, and preferably in shape, to the hearth of an open hearth furnace. the tilting type, the body being mounted on a cradle 16 which rests on rollers 17 on suitable stationary trackways 18. 19. indicates a pouring spout adjacent to the top line of the bath through which the slag and molten metal may be poured off by tilting the furnace.

The furnace shown is of Extending transversely of the furnace body a suitable distance below the basin are two or more open ended passageways bounded by split tubes 20 extending clear across the body. Occupying these tubes are the cores with the primary windings. As

shown, the cores 21, preferably laminated by being made of sheets of proper metal, are connected at their ends by yoke pieces 22, making a continuous magnetic circuit. These cores are supported centrally within the tubes 20 by suitable means, as, for example, the brackets 2ei secured to the outside of the furnace. Surrounding the cores some distance from the-tubular walls 20 are the primary windings 25. The space between the primary windings and the tubes is provided for ventilation. This ventilation may be insured by a blast of air through such space, and the drawing shows an air pipe 30' having branches 31 discharging into the two annular spaces within the tubes.

Formed in the body of the furnace in the particular embodiment illustrated is a conduit for metal extending around the sides and bottom of the primary windings and communicating at its upper ends with the bath. This conduit consists of the two downwardly extending tubular passageways 35, the central passageway 36 and the passageways 37 connecting the central passageway with the two extreme passageways.

All of these passageways are located in a vertical plane substantially at the center of the furnace. Accordingly, there is about each primary a vertical annular secondary circuit, the top portion of which consistsof a portion of the bottom of the bath and the sides and bottom of which consist of metal in the passageways 35, 37, 36.

Now it results from the above described construction that when alternating current is passed through the primary windings, a

current is induced in the secondary circuit and this circuit is adapted to heat such secondary circpit so that at least the portion in the bath comes to the fusing point. The metal in the passageways may be similar to that in the bath, so that it will also fuse. In such case, by making the passageway 36 of different cross sectional area than the combined two .passageways 35, the fusible material in the passageway 36 (on account of the different electrical resistance) receives a different temperature than that in the passageways 35 or 37, so that there is an annular circulation of the fusible material constituting the secondaries. In the drawings the central passageway is smaller than the combined extreme passageways, giving the direction of circulation indicated by the arrows in Fig. 2. This circulation, together with the constant heating of the bath from the bottom, causes a circulation throughout the bath, producing a thorough mixing of the molten metal, and a consequent great reduction of the time required for the refining process.

It is to be understood that, in starting the furnace having the operation just described, filings or chips are placed in the bottom of the bath and in the passageways, and the current passed through the primary causes the fusing and circulation of the secondary as described; or molten metal to be further heated and refined may be poured into the furnace to fill the passageways and basin. 38, in Fig. 2, indicates a normally closed tap hole for draining the passageways for repairs or at the end of a campaign.

If desired, suitable plates, indicated at 40 in Figs. 2, 3 and 5 may be embedded in the walls of the furnace at the sides of the basin and receiving either direct or alternating current may additionally heat the bath and slag by resistance. The width of the basin can be so selected that the desired resistance to the passage of the current may be obtained between the opposite plates 40. To enable the passage of this current from the embedded plates after the furnace walls have become hot, magnesite is preferably employed for lining the side walls of the bath; In fact, thewhole body of the fur nace'within the metallic shell may conveniently be made of magnesite.

In addition to the advantages heretofore referred to of the unobstructed bath and the heating from the bottom, the open bath is not only easy to work but enables easy repair of the linings, since the entire slag line, where the greatest scarification occurs, is within reach of the furnace doors. The entire hearth bottom and sides may be con: veniently repaired while the furnace is hot, and the entire slag line be repaired and fettled while running, as in the open hearth furnace. It should be noted that in my furnace the extent of the slag line and the surface of the bath exposed to the atmosphere are greatly less than in a furnace of the same capacity where the secondary circuit consists of an annular bath of metal lyingin a horizontal plane. This results in minimizing the scarification and the loss from radiation. Furthermore, from an operating standpoint, this free bath has the advantage of being of the same general character as the .open hearth with which the workmen are already familiar.

The location of the core and primary below the bath not only produces better circulation by heating the molten metal from the bottom while keeping the primary cool, but simplifies the ventilation of the primary and facilitates repairs to the roof and working parts of the furnace, since they are entirely independent of and away from the core and primary,'which are located below the usual working platform surrounding the furnace. This location of the core and primary coil below the bath and away from the upper portion of the furnace and the working parts makes repairs to the core and primary convenient and possible without disturbing the roof or walls of the furnace.

Having thus described my invention, what I claim is:

1. The combination, with a furnace basin, of an induction coil having a closed magnetic core lying in a substantially horizontal plane, a primary winding about such core, the secondary of said coil consisting of the bottom portion of the bath of molten metal within the basin, and a conductor of electricity outside of the basin completing the annular circuit with such bottom portion.

2. The combination, with a furnace basin, of an induction coil having a closed magnetic core lying in a substantially horizontal plane, a primary winding about said core, and an annular secondary lying in an up and down plane and including a bottom portion of the bath of molten metalwithin the basin.

8. The combination, with a furnace basin, of an induction coil, the core of which is annular and lies in a substantially horizontal plane, and the secondary of which consists of a portion of the bath of molten metal within the basin, and a conductor of electricity beneath the basin.

4. The combination, with a furnace basin, of an induction coil having a substantially horizontal annular core and a. primary winding located beneath said basin, the secondary of such coil consisting of a portion of the bath of molten metal along the bottom of the basin, and a multiple U-shaped conductor surrounding the core and primary winding and at its upper ends joining the bath of molten metal.

5. The combination, with a furnace basin, of a horizontal annular core beneath it, a primary winding surrounding such core," and a U-shapecLpassageway in the furnace body about a leg of the 'core, said passageway holding a conductor of electricity which with a portion of the bathof molten metal constitutes an annular secondary.

6. The combination, witha furnace body having a basin and a transverse tubular opening beneath the basin, a closed magnetic core lying in a substantially horizontal plane and having one leg within such opening and a surrounding primary winding within such opening, and a passageway in the furnace body about the tubular opening terminating at its upper ends at the bottom of the basin.

7. The combination, with a furnace body having a basin, a tubular opening through the body beneath the basin, a horizontal closed magnetic core having a leg and a primary winding within such opening, and, a

' horizontal passageway lying in a vertical plane and located within the body extending about the opening and terminating at its upper ends at the bottom of, the basin whereby said passageway is adapted to inclose conducting material which, with a bottom portion of the bath in the basin, makes an annular secondary circuit.

8. The combination, with a furnace basin, of an induction coil having a closed magnetic core lying in a substantially horizontal plane an annular secondary which includes a portion of the bath ofmolten'metal in the basin, and means for causing the material of said secondary to automatically circulate.

9. The combination, with a furnace basin, of the core and primary of an induction coil, said core constituting a closed magnetic circuit and lying in a substantially horizontal plane, and a U-shaped passageway located beneath the basin and adapted to hold material which, with a portion of the bath of molten metal in thebasin, constitutes an annular secondary of the induction coil.

10. The combination, with a furnace basin, of an induction coil having a horizontal annular core and primary, and a U-shaped passageway extending in the up and down direction and terminating at its upper ends at the bottom of the basin, the material in the passageway and a portion of the material in the bath constituting an annular secondary circuit, the legs of such passageway being of different cross section to compel the material therein to receive different temperatures and thereby circulate.

11. The combination, with a furnace basin, of a plurality of primary coils beneath the same, U-shaped passageways extending around the individual primary coils and terminating at their upper ends at the bottom of the basin, said passageways having a com' mon leg between the coils.

12. In an electric furnace, the combination, with a furnace basin, of cores located side by side horizontally beneath the basin, primary windings around said cores, and passageways extending around said windings respectively and communicating with the basin from outside of the cores and from between them, the passageway between the cores being of different cross sectional area than the two outside passageways.

'13. In an electric furnace, the combination of a furnace body having a basin and tubular openings extending through the body below the basin and open at their ends, cores occupying such openings respectively magnetic, members connecting the ends of said cores to form a horizontal closed magnetic circuit, primary windings on such cores within the tubular openings, means for supplying air to the annular spaces around the primaries within the openings, and passageways extending retom.

14. In an electric furnace, the combination, with a furnace body having a basin and two transverse tubular openings extending through the body below the basin, of a pair of cores occupying such openings respectively and connected by cross bars beyond the sides of the furnace body, primary windings on such cores within the tubular openings, and a pair- "of vertically disposed U- shaped passageways extending around the two tu ular openings respectively, said passagewafys having their outermost legs communicating with the basin near its ends and their innermost legs merging into one common leg communicating with the basin near its center.

15. In an electric furnace, the combination, with a furnace body having a basin and two transverse tubular openings extending through the body below the basin, of a pair of cores occupying such openings respectively, primary windings on such cores within the tubular openings, and a pair of passageways lying in a vertical plane and extending in a U-shape around the two tubular openings respectively, said passageways having their outermost legs connected with the basin near its ends and their innermost legs merging into one common leg connected with the basin near its center, said common leg'of the passageways having a cross sectional area which is different from the combined area of the two extreme legs.

16. In an electric furnace, the combina- 40 tion, with a furnace body having a basin v of two parallel horizontal open ended split tubes located in the body below the basin, a pair of cores occupying such tubes respectively and connected by cross bars beyond the sides of the furnace body, means for supporting such cross bars independently ofthe tubes, primary windings on such cores within the tubes, and a pair of passageways within the furnace body extending around the two tubes respectively, said passsageways lying in a vertical plane and each having a leg communicating with the basin near an end thereof and having between the cores a common central leg communicating with the basin near its center, saidcommon central leg of the passageways having a cross sectional area which is different from the combined area of the two extreme legs.

17. The combination, with a furnace basin adapted to contain molten metal, of an induction coil having an annular secondary which includes a portion of the bath of molten metal in the basin and a conductor of electricity in a U-shape below such basin, and a tap opening for molten metal leading from the basin in position to allow discharge of metal from the basin without breaking the secondary circuit.

18. The combination, with afurnace basin adapted to. contain molten metal, of doorways opening into the space above the basin and providing means for adding slag-forming materials and working the material in the basin, means for closing suchdoorways, and an induction coil having a closed mag- .netic core lying in a horizontal plane and one or more primary windings therefor and whose secondary is located in an up and down plane and comprises a bottom portion of the bath of molten metal, and a conductor of electricity below such bath.

In testimony whereof, I hereunto affix my signature in the presence of two witnesses.

WALTER N. CRAFTS.

Witnesses:

ALBERT I-I. BATEs, BRENNAN B. WEST. 

